我在尝试在Hadoop中启动datanode时遇到一些问题,从日志中我可以看到datanode启动了两次(部分日志跟随)：

2012-05-22 16:25:00,369 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: STARTUP_MSG: 
/************************************************************
STARTUP_MSG: Starting DataNode
STARTUP_MSG:   host = master/192.168.0.1
STARTUP_MSG:   args = []
STARTUP_MSG:   version = 1.0.1
STARTUP_MSG:   build = https://svn.apache.org/repos/asf/hadoop/common/branches/branch-1.0 -r 1243785; compiled by 'hortonfo' on Tue Feb 14 08:15:38 UTC 2012
************************************************************/
2012-05-22 16:25:00,375 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: STARTUP_MSG: 
/************************************************************
STARTUP_MSG: Starting DataNode
STARTUP_MSG:   host = master/192.168.0.1
STARTUP_MSG:   args = []
STARTUP_MSG:   version = 1.0.1
STARTUP_MSG:   build = https://svn.apache.org/repos/asf/hadoop/common/branches/branch-1.0 -r 1243785; compiled by 'hortonfo' on Tue Feb 14 08:15:38 UTC 2012
************************************************************/
2012-05-22 16:25:00,490 INFO org.apache.hadoop.metrics2.impl.MetricsConfig: loaded properties from hadoop-metrics2.properties
2012-05-22 16:25:00,500 INFO org.apache.hadoop.metrics2.impl.MetricsSourceAdapter: MBean for source MetricsSystem,sub=Stats registered.
2012-05-22 16:25:00,500 INFO org.apache.hadoop.metrics2.impl.MetricsSystemImpl: Scheduled snapshot period at 10 second(s).
2012-05-22 16:25:00,500 INFO org.apache.hadoop.metrics2.impl.MetricsSystemImpl: DataNode metrics system started
2012-05-22 16:25:00,512 INFO org.apache.hadoop.metrics2.impl.MetricsConfig: loaded properties from hadoop-metrics2.properties
2012-05-22 16:25:00,523 INFO org.apache.hadoop.metrics2.impl.MetricsSourceAdapter: MBean for source MetricsSystem,sub=Stats registered.
2012-05-22 16:25:00,523 INFO org.apache.hadoop.metrics2.impl.MetricsSystemImpl: Scheduled snapshot period at 10 second(s).
2012-05-22 16:25:00,524 INFO org.apache.hadoop.metrics2.impl.MetricsSystemImpl: DataNode metrics system started
2012-05-22 16:25:00,722 INFO org.apache.hadoop.metrics2.impl.MetricsSourceAdapter: MBean for source ugi registered.
2012-05-22 16:25:00,724 INFO org.apache.hadoop.metrics2.impl.MetricsSourceAdapter: MBean for source ugi registered.
2012-05-22 16:25:00,727 WARN org.apache.hadoop.metrics2.impl.MetricsSystemImpl: Source name ugi already exists!
2012-05-22 16:25:00,729 WARN org.apache.hadoop.metrics2.impl.MetricsSystemImpl: Source name ugi already exists!
2012-05-22 16:20:15,894 INFO org.apache.hadoop.hdfs.server.common.Storage: Cannot lock storage /app/hadoop/tmp/dfs/data. The directory is already locked.
2012-05-22 16:20:16,008 ERROR org.apache.hadoop.hdfs.server.datanode.DataNode: java.io.IOException: Cannot lock storage /app/hadoop/tmp/dfs/data. The directory is already locked.
        at org.apache.hadoop.hdfs.server.common.Storage$StorageDirectory.lock(Storage.java:602)
        at org.apache.hadoop.hdfs.server.common.Storage$StorageDirectory.analyzeStorage(Storage.java:455)
        at org.apache.hadoop.hdfs.server.datanode.DataStorage.recoverTransitionRead(DataStorage.java:111)
        at org.apache.hadoop.hdfs.server.datanode.DataNode.startDataNode(DataNode.java:385)
        at org.apache.hadoop.hdfs.server.datanode.DataNode.<init>(DataNode.java:299)
        at org.apache.hadoop.hdfs.server.datanode.DataNode.makeInstance(DataNode.java:1582)
        at org.apache.hadoop.hdfs.server.datanode.DataNode.instantiateDataNode(DataNode.java:1521)
        at org.apache.hadoop.hdfs.server.datanode.DataNode.createDataNode(DataNode.java:1539)
        at org.apache.hadoop.hdfs.server.datanode.DataNode.secureMain(DataNode.java:1665)
        at org.apache.hadoop.hdfs.server.datanode.DataNode.main(DataNode.java:1682)

我在网上搜索过,我找到了this question,但是我没有使用conf / hdfs-site.xml覆盖任何内容,如下所示,因此Hadoop应该使用默认值(如here所述)不会导致任何失败的锁定.
这是我的conf / hdfs-site.xml：

<?xml version="1.0"?>
<?xml-stylesheet type="text/xsl" href="configuration.xsl"?>

<!-- Put site-specific property overrides in this file. -->

<configuration>
  <property>
    <name>dfs.replication</name>
    <value>2</value>
    <description>Default block replication.
    The actual number of replications can be specified when the file is created.
    The default is used if replication is not specified in create time.
    </description>
  </property>
</configuration>

这是我的conf / core-site.xml：

<?xml version="1.0"?>
<?xml-stylesheet type="text/xsl" href="configuration.xsl"?>

<!-- Put site-specific property overrides in this file. -->

<configuration>
  <property>
    <name>hadoop.tmp.dir</name>
    <value>/app/hadoop/tmp</value>
    <description>A base for other temporary directories.</description>
  </property>

  <property>
    <name>fs.default.name</name>
    <value>hdfs://master:54310</value>
    <description>The name of the default file system.  A URI whose
    scheme and authority determine the FileSystem implementation.  The
    uri's scheme determines the config property (fs.SCHEME.impl) naming
    the FileSystem implementation class.  The uri's authority is used to
    determine the host, port, etc. for a filesystem.</description>
  </property>
</configuration>

这是hadoop / conf / slaves的内容：

master
slave

解决方法:

>停止datanode
>从dfs数据目录中删除in_use.lock文件
>位置并启动datanode

它应该工作得很好